The present invention relates to a construction similar to that disclosed in our earlier U.S. Pat. No. 3,838,706, the entire disclosure of which is incorporated herein by reference.
The construction disclosed in that patent is a conduit closure, especially for use to prevent both backflow and also the escape of noxious gases. The closure includes a downwardly extending internal conduit and a swingable cover, mounted for swinging movement on a horizontal shaft located to the side of the internal conduit. A counterweight connected to the cover by lever arms normally urges the cover upward into its closed position. When in its closed position, the upper rectangular rim of the cover seal-tightly engages a sealing ring. The sealing ring is located exteriorly of the internal conduit, at an elevation higher than the bottom end of the internal conduit. The cover is generally shovel-shaped and has an inclined bottom wall which, when the cover is closed, slopes upward in the direction away from the aforementioned shaft and terminates at a spillover edge. The cover collects incoming fluid, and when a certain amount of fluid has been collected spontaneously and quickly swings down into its open position. The amount of fluid which triggers this quick downswing is such that, when this amount of fluid is collected, the upper level of the body of fluid is located beneath the bottom end of the aforementioned internal conduit. When the cover is in its upwardly swung, closed position, it, the mounting shaft, and the counterweight are all located at about the same height. The disposition of the latter three parts is such that, when the quantity of water in question has been accumulated, the biasing force of the counterweight is overcome; as the counterweight begins to swing upward, the biasing force it exerts (such as to tend to close the cover) decreases, the furthermore, the collected water displaces itself towards the spillover edge of the cover thereby exerting a greater opening force, so that the opening movement of the cover is very quick and positive.
This construction has a number of advantages. The cover opens, only briefly, to discharge collected fluid when the predetermined quantity of fluid has accumulated. When in the open position, the cover is located out of the way of the descending fluid. Furthermore, after such discharge, if a sizable flow of fluid is not entering the closure, the cover closes again completely, without dwelling in intermediate positions. Accordingly, the cover is normally closed, when it opens does so only briefly to discharge an accumulated amount of water, and when it is thusly open for short periods presents little opportunity for the escape of noxious or polluting gases. Furthermore, relatively large solid bodies such as stones or clumps of leaves easily pass through the closure when the cover is in open position. Accordingly, there is no danger that such solid bodies will become lodged between the cover and its cooperating sealing ring, which could result in the continual escape of gases through the conduit closure. Furthermore, because the accumulated fluid cannot rise to the level of the sealing ring, the latter is protected from being frozen solid onto the cover in winter conditions.
However, it has been found that despite the above-enumerated advantages inherent in this construction, with long use the reliability of the sealing action which prevents the escape of gases becomes less certain and positive. In particular, it has been found that loss of seal-tightness can develop at those portions of the upper rim of the cover which are adjacent to the shaft on which the cover is swingably mounted. This is because, at these locations, the sealing force with which the rim of the cover presses against the sealing ring is not sufficient to assure that, as the mountings of the cover wear and the sealing ring looses some of its elasticity, the sealing action will nevertheless continue to be positive and complete. The counterweight which biases the cover to its closed position does not help in this respect. The upwards force transmitted to the cover by the counterweight is mainly applied, for various reasons, to the part of the cover remote from the mounting shaft. Certainly, upwards force is also transmitted, by lever action, to the part of the cover close to the mounting shaft. However, at this location, i.e., near where the cover and counterweight are supported for swinging movement, the weight of the cover and counterweight pulls down. As a result, if there is any play whatsoever in the mountings of the cover and counterweight, this downwards force can pull this part of the cover away from its cooperating part of the sealing ring. Accordingly, in the region near the mounting shaft, there sets in a loss in the elastic compressibility of the sealing ring and an actual increase of the play with which the cover and counterweight are swingably mounted.